This also creates a g3doc directory under pc/
Bug: webrtc:12552
Change-Id: I0913c88831658776a0f02174b57b539ac85b4a9f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215077
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33718}
